‘If consciousness is radically separate from the world, you can imagine it eventually flying off to heaven or being uploaded into a computer. In short, evading death.’
Photograph: annedde/Getty Images

Humankind has been reflecting on consciousness from the moment thought became possible. What is this business of experiencing colour, touch, taste, sound, smell? How does it happen, and where? Is the world as we experience it? There’s hardly a philosopher hasn’t made a contribution, or, more recently, a neuroscientist.

To get your bearings in the literature, then, it’s not a bad idea to divide the field into those who think consciousness is all internal to the body, those who claim it involves our bodies and objects we engage with, and those who say our experience is external – one with the things experienced.

Internalists dominate. You can go back to Galileo in The Assayer telling us that colour, smell and taste only exist inside us, or again, Descartes in his Meditations deciding that thought, perception and selfhood are non-physical substances connected to the physical world by the pineal gland at the bottom of the brain. One great advantage of internalism is that if consciousness is radically separate from the world, you can imagine it eventually flying off to heaven or being uploaded into a computer. In short, evading death.

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Neuroscientists are almost all internalists. For an easy-to-read rehearsal of present orthodoxy, try David Eagleman’s The Brain: The Story of You. There is much mind-boggling information about the complexity of our 85bn neurons and what they are up to when we experience this or that, the so-called neural correlates of consciousness. Christof Koch’sConsciousness: Confessions of a Romantic Reductionist lays out the claim that we are our brains and that knowledge of brain “wiring” and activity will eventually allow us to know what a person is thinking by examining brain activity.

How that wiring becomes experience is something Giulio Tononi tries to explain in the somewhat fantastical Phi: A Voyage from the Brain to the Soul. He believes consciousness arises when an extraordinary level of interconnectedness produces something new and extra called “integrated information”. Why this should be the case he does not say, but the book is fascinating for the writer’s determination to reduce experience to numbers of neurons and synapses.

The most serious and celebrated contemporary internalist is Daniel Dennett, who in Kinds of Minds: Toward an Understanding of Consciousness builds up an evolutionary view of consciousness as something organisms developed thanks to their “intentional” engagement with the world, a phenomenon made infinitely more powerful in humans, he believes, because of the discovery of language.

‘Riccardo Manzotti denies that there is anything in the head but neurons and their electrochemistry.’ Photograph: Alamy Stock Photo

Turning to the “enactivists”, who would have consciousness as a collaboration between brain, body and object, the best books I have read are Andy Clark’s Supersizing the Mind: Embodiment, Action, and Cognitive Extension, and W Teed Rockwell’s Neither Brain Nor Ghost: A Nondualist Alternative to the Mind-Brain Identity Theory. Clark is the more cautious, mixing the idea of a representation in the head with the notion that the objects we handle and memory props we use – notebooks, computers, phones – become part of our consciousness. Rockwell is more adventurous; there is no “magic threshold”, he boldly declares, between the body and the world; consciousness of an object cannot be separated from it.

Boldest, however, is philosopher and robotics engineer Riccardo Manzotti. In The Spread Mind: Why Consciousness and the World Are One he strenuously denies that there is anything in the head but neurons and electrochemistry; the experience that constitutes our lives lies outside, one with the object, which is as it is thanks to the presence of our bodies and indeed our neurons. What is extraordinary is how systematically and engagingly Manzotti is able to reconcile this externalist and physicalist approach with the findings of neuroscience, the theory of relativity and even quantum mechanics.